5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Wednesday, 19 November 2003: 3:45 PM
A Climatological Study of the Keetch/Byram Drought Index in the Hawaiian Islands
Pao-Shin Chu, University of Hawaii at Manoa, Honolulu, HI; and K. P. Dolling and F. M. Fujioka
Poster PDF (1.3 MB)
The United States experience damaging wildfires on a yearly basis. Most areas in the United States experience periodic droughts. Periods without substantial rain are part of the natural annual cycle as well as part of natural long-term fluctuations. Incorporating daily maximum temperatures and daily rainfall amounts, the Keetch and Byram Drought Index describes the amount of soil moisture available. Measurements of soil moisture are essential information in fighting wildfires.

The Hawaiian Islands have unique and varied microclimates. The localized nature of these microclimates means that they will be affected differently by the larger-scale climatic influences of the region. Having established a strong link between KBDI and TAB (total acres burned), it becomes important to understand how different climatic fluctuations affect KBDI.

Harmonic analysis is used to investigate the annual cycle of the KBDI at individual stations. A comparison of the annual cycle in rainfall is made with the index. The annual cycle of KBDI is found to lag the annual cycle of rainfall by one to three months. The variability of the KBDI on different time scales is investigated through the use of spectral analysis. Individual stations are found to have different sensitivities to large-scale climatic fluctuations. An El Nino signal (forty to fifty month cycle) is clearly linked to leeward stations using a band pass filter.

Atmospheric circulations are also investigated with respect to the KBDI. Reference stations from previous analyses are used. A composite is constructed for each of the four seasons. The upper and lower quartiles of each seasonal composite are found. Surface pressure, surface wind, 200 mb winds, and 500mb geopotential height fields are investigated for seasons in the upper and lower quartile of KBDI.

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